The invention relates to a telecommunication system which integrates a mobile network with a wireline network.
In a conventional wireline network, for example one of the type which is known as the “Plain Old Telephone System” (POTS), subscribers are provided with a directory number for a location in the system i.e. an access point where a fixed terminal of the subscriber is connected to the system, and calls are switched through to the location indicated by the directory number. Customer services, billing procedures and enhanced services to which the user has subscribed are organized on the basis of the principle that the service is tied to the fixed access point.
In contrast, a mobile network has to be organized in view of the fact that access is not a through fixed access point but through mobile terminals. As a consequence, services are stored and provisioned on a single node in the netwsork and distributed on an “as needed” basis. The subscriber is identified by a unique and permanent identifier, for example by the “International Mobile Subscriber Identity (IMSI) in accordance with existing international standards. This identifier may for example be stored in a memory which is part of the mobile device itself or in a separate insertable memory module, for instance a Subscriber Identity Module (SIM) in an integrated chip card as is known from the European GSM mobile telecommunication system. Communication between the mobile device and the stationary part of the network is achieved through an air link, i.e. by radio transmission. Radio transmission system protocols are used to identify the subscriber from the information encoded on the SIM card. Services which the user has subscribed to can be derived from the same provisioning node. They are linked against the subscriber ID that is also stored on the SIM card.
In a cellular mobile network such as GSM, the air link connects the mobile device to one of a plurality of stationary transceivers each of which provides radio coverage for a certain area (cell). The transceivers are interconnected by the mobile network which may be in the form of a packet network or in the form of a switched node type network as in GSM. The following description will refer to the GSM system as a typical example of a prior art mobile network.
Typically, a plurality of transceivers are controlled by a node which is called Mobile Services Switching Center (MSC). The MSCs can communicate with each other and with a central register which is called “Home Location Register” (HLR). This HLR stores the subscriber Identifiers (IMSIs) of all subscribers along with location information and additional information which is needed among others for identifying the services to which the user has subscribed. Associated with each node (MSC) is a so-called Visitor Location Register (VLR) which stores the necessary data from the Home Location Register (HLR), but only for those subscriber identifiers (IMSIs) of the mobile devices that are presently “visiting” the area of radio coverage controlled by the MSC. When the mobile device enters into the area of radio coverage of another MSC, this has to be signaled to the Home Location Register (HLR), and a copy of the data file pertaining to this device is transferred into the Visitor Location Register (VLR) associated with the new MSC. Thus, the HLR can keep track of the location of all mobile devices. In a call setup procedure, the HLR is queried by a Gateway MSC (GMSC) of the operator's network as to the current location of the called mobile device, and the HLR returns a “Mobile Subscriber Roaming Number” (MSRN) under which the called device can currently be reached. This MSRN is temporarily assigned to the called device by the MSC (terminating MSC) which is at that time visited by the called device. Then, the MSC that is in charge of the calling party (originating MSC) uses the MSRN for directly contacting the terminating MSC.
A mobile network is typically linked to other networks. e.g. to a Public Switched Telephone Network (PSTN), by mans of a gateway, e.g. a gateway MSC (GMSC), so that it is possible to make a call from the mobile network into the PSTN and vice versa. On the other hand, a mobile subscriber will normally have direct access to a PSTN through a fixed terminal, e.g. an analog telephone or an ISDN Basic Rate Interface (BRI). This co-existence of mobile networks and wireline networks has several drawbacks. From the viewpoint of the user, a main drawback is that he has to subscribe to two different networks, one mobile network and one wireline network. In addition to increased costs, this involves the inconvenience that the user has to cope with different sets of services offered by the operators of the two networks, and the service profiles to which the user has subscribed in the two networks will generally not be consistent with each other. From the viewpoint of the operator, a main drawback can be seen in the necessity to establish and run two separate networks, a mobile network and a wireline network, in order to provide full service to the customers. Although many services will be similar or even identical in the mobile network and in the wireline network, these services must be developed and implemented separately in the two networks. It would therefore be desirable to provide for more “convergence” between the two types of telecommunication networks and, ideally, to integrate mobile network facilities and wireline network facilities into a single network which is organized under a unique scheme and includes service facilities that may be used in common for the mobile part and the fixed line part of the system.
One approach to integrate fixed wireline networks and mobile networks is based upon an Intelligent Network (IN) system that is provided “on top” of the two networks. Then, if a subscriber wants to have one common directory number (DN), an identical service set and a consistent service profile for both networks, all services including the DNs have to be under control of the IN system. The underlying fixed and mobile networks are just used as vehicles to get the data to and from the IN system. This, however, has the drawback that the operator still has to manage two different networks and, in addition, the IN system, which leads to increased costs. Moreover, the expensive available service infrastructure present in the fixed and mobile networks is only partially used. Although it would be possible to convert services offered in the underlying fixed and mobile networks to the IN system, this solution is in most cases not practicable for cost reasons.
Another approach which achieves, to a certain extent, an integration of fixed lines into a mobile network, has been described in EP-A-0 779 757. Here, the fixed terminals are connected through fixed lines to an interface unit which, from the perspective of the MSC, behaves like a transceiver or like a so-called Base Station Subsystem (BSS) controlling one or more transceivers. The subscriber identifiers for the fixed line subscribers are encoded on SIM cards just as the identifiers for mobile subscribers, and these SIM cards are inserted in the fixed terminal devices. As a consequence, the fixed terminal devices must be equipped with a card reader in order to be able to connect the mobile network. The main disadvantage of this approach is that non-standard fixed line signalling has to be used.
EP-A-0 923 258 describes a similar solution which is also based on the use of an interface unit which is called a “Fixed Access Controller” (FAC). This FAC may be integrated in the mobile access node MSC or may be incorporated in the system somewhere between the MSC and the fixed terminals. The necessity to physically provide SIM-cards and SIM-card readers in the fixed terminal devices is avoided by employing so-called virtual SIMs (VSIMs) which may be implemented in the fixed access controller FAC.
In this known system, specific measures are described for fully exploiting the larger bandwidth of fixed lines in comparison to wireless connections. Since the air link represents a bandwidth bottleneck, the communication among the various MSCs occurs at a higher transmission rate (e.g. 64 kB/s) than the communication over the air link (e.g. at 16 kB/s), and the system includes certain interworking functionality for compression of voice data and for adapting the transmission rates. This interworking functionality may be implemented in the MSC or somewhere downstream towards the air link. If non-voice data (e.g. fax) are to be transmitted to a fixed line access, this interworking functionality is not needed and is even undesirable in view of the achievable transmission rate. This is why the known system provides means for bypassing the interworking functionality in case of (non-voice) data calls.
Since the mobile network and the wireline network use different signaling protocols, the interface unit, e.g. the FAC, has to provide for protocol conversion. On the other hand, since the administration system of the mobile network treats the fixed access subscribers (represented by the virtual SIMs) as if they were mobile subscribers, the messages from the mobile network to the fixed terminal or vice versa, or at least portions of these messages, should be transmitted transparently through the wireline network.
In some of the embodiments disclosed in EP-A-0 923 258 this is achieved by providing a first interface unit between the mobile network and the wireline network and a second interface unit between the wireline network and the fixed terminal. Then, messages from the mobile network to the fixed terminal are encapsulated in the first interface unit and, conversely, messages from the fixed terminal to the mobile network are encapsulated in the second interface unit. If the wireline network is a Public Switched Telephone Network (PSTN), each of the two interface units will have a directory number within the PSTN system. However, these directory numbers are “invisible” for the mobile network, i.e. they are not stored in the Home Location Register (HLR) of the mobile network.
In another embodiment, the fixed access terminal is an ISDN telephone, and interfacing to the mobile network is achieved by means of a converter which may be owned or rent by the fixed access subscriber and which emulates all the functions of a mobile transceiving device and terminates all mobile network signaling (e.g. DTAP signaling) from the MSC and converts it to ISDN Q931 signaling for the subscriber's terminal equipment. Since an ISDN basic rate interface comprises two traffic channels, the converter stores two different subscriber Identifiers (IMSIs), one for each channel. These IMSIs are also stored in the HLR of the GSM mobile network, and they are treated there like IMSIs of two (different) mobile subscribers. The HLR does not “know” the ISDN directory number assigned to this access.
Since, in these known systems, the HLR or, more generally, the administration system of the mobile network does not distinguish between a true mobile access and a virtual mobile access which in fact represents a fixed line access, the mobile network is not capable of providing all the services that are commonly provided in a wireline network, and integration of lines and services can only be achieved to a limited extent. Moreover, provisioning of lines and services for the fixed line subscribers is effected mainly on the level of the MSCs or lower, i.e. in a decentralized way. This has the drawback that provisioning of fixed line access to the mobile network is difficult to manage, and when a user has subscribed to both a mobile access and a fixed line access, consistency of the respective service profiles cannot be guaranteed.